1. Field of the Invention
The invention relates to condensation crosslinkable compositions based on organosilicon compounds which have controllable modulus, to their preparation, and to their use as sealants.
2. Background Art
Single-component sealants which are storable with the exclusion of water and which can be vulcanized to elastomers at room temperature on ingress of water are known. These products are used in large amounts, for example, in the construction industry. These mixtures are based on polymers which are terminated by silyl groups bearing reactive substituents such as OH groups, or hydrolyzable groups such as alkoxy groups, and also generally include crosslinkers, for example alkoxysilanes.
For joint sealants in particular, it is desired that the modulus, i.e. the stress value at 100% elongation of a test specimen, is low, so that minimum forces act on the joint flanks. Another desirable property relates to the uniform curing through the sealants after the application, so that the hardness differences between the upper and lower side of the joint are minimal.
The preparation of oligomeric crosslinkers, obtainable from cohydrolysis of monomeric crosslinkers, for example according to U.S. Pat. No. 5,282,998 by means of water and acidic catalyst, or, as described in U.S. Pat. No. 4,950,779, by means of formic acid and strongly acidic catalyst, has been known for some time. U.S. Pat. No. 6,395,856 describes the reaction of vinyltrialkoxysilanes with formic acid, H-silanes or higher alcohols. In all of these products, the content of hydrolyzable groups is quite high. Also, the cleavage products and unconverted monomers have to be removed.
U.S. Pat. No. 5,837,784 describes the reaction of MQ resins with alkoxysilanes in the presence of basic catalysts, D and T units being present only to a maximum degree of 20%.